The efficiency or functionality of many types of semiconductor devices can be enhanced by utilizing a substrate or selected device layers having a highly structured surface. As used herein, the term “highly structured surface” refers to any surface, substrate or layer which has structure, surfaces, faces or other topographic features exhibiting non-planar contours in three dimensions. For example, a highly structured surface may include but is not limited to an array or random collection of pillars, pyramids, spikes, valleys, holes, channels, macroscopic roughness or other surface structure which extends away from a generally planar overall structure.
Devices and layers which have a highly structured surface will feature substantially greater actual surface area when compared to a relatively smooth and planar unstructured surface of corresponding overall size. In many instances the increase in overall surface area provided by an appropriately designed highly structured surface can be quite dramatic. Accordingly, substrates or layers featuring a highly structured surface are useful in technologies where chemical or photonic activity occurs over a surface area, including but not limited to photovoltaic cells, batteries and fuel cells.
Most commercially practical processes for the application, deposition or growth of a layer or coating of a selected semiconductor material on to a substrate or underlying layer cause the deposition of material substantially along a line-of-sight between the deposition material source (also known as the target) and the deposition substrate or device. A highly structured surface will necessarily include surfaces which are wholly or partially shaded from the deposition material source or which are presented to the deposition material source at a relatively steep angle. These surfaces, which are defined as “indirect deposition surfaces” herein, are difficult or impossible to coat with an effective thickness of material according to conventional line-of-sight deposition techniques. Material inconsistency, gaps, openings, thin areas or uncoated areas deposited on indirect or shaded surfaces will typically compromise the overall efficiency and functionality of a device featuring semiconductor layers deposited on a highly structured surface.
The embodiments disclosed herein are intended to overcome one or more of the limitations described above. The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.